Density-Matched Suspensions and Associated Methods

ABSTRACT

Of the many compositions and methods provided herein, an example method includes a method of treating a subterranean formation that comprises combining components comprising water and a density-matched suspension to prepare a treatment fluid, wherein the density-matched suspension comprises a suspending liquid and a solid particle suspended in the suspending liquid, and introducing the treatment fluid into a well bore. An example composition includes a suspension that comprises a suspending liquid comprising a hydrophobic liquid, wherein the hydrophobic liquid hydrolyzes when placed in contact with an aqueous fluid to form hydrophilic products, and a solid particle suspended in the suspending liquid, wherein the suspension is a density-matched suspension.

BACKGROUND

The present invention relates to density-matched suspensions and, moreparticularly, in certain embodiments, to density-matched suspensionsthat comprise a solid particle suspended in a suspending liquid andassociated methods of use.

Suspensions may be used in any number of applications where it may bedesirable to suspend a solid particle in a suspending liquid forextended periods of time. For example, such applications may includecosmetics, pharmaceuticals, foodstuffs, agricultural products (e.g.,fertilizers, pesticides, etc.), decorative mixtures, and downholeapplications. In downhole applications, for example, downhole additives(such as water-soluble polymers) may be suspended in inert organicliquids to facilitate their handling and mixing with well treatmentfluids, such as cement compositions.

In general, a suspension is typically formulated so that the solidparticle should not undesirably settle out of the suspending liquid. Toprevent sedimentation of the solid particle, the suspension typicallymay rely on viscosity. As used herein, a suspension that relies at leastsubstantially on viscosity to prevent sedimentation of the solidparticle is referred to as a “viscosity-controlled suspension.” By wayof example, the liquid generally may have a viscosity sufficient to slowthe sedimentation rate of the solid particle, which typically has adensity greater than the suspending liquid. To provide the necessaryviscosity, a suspending agent (e.g., hydrophobic polymers, organophilicclays, etc.) may be included in the viscosity-controlled suspension.However, reliance on viscosity to prevent sedimentation may beproblematic. For instance, the viscosity of the suspending liquid maychange with time such that the suspending liquid may not have asufficient viscosity prevent the undesired sedimentation of the solidparticle. Accordingly, the viscosity-controlled suspensions may not havethe desired shelf life.

As previously mentioned, downhole additives may be suspended in inertorganic liquids to facilitate their handling and mixing with welltreatment fluids. For example, fluid-loss-control additives (such aswater-soluble polymers) may be suspended in an organic liquid tofacilitate their handing and mixing with a cement composition. Suchsuspensions generally contain a high concentration of thefluid-loss-control additive, the organic liquid (e.g., mineral oil), asurfactant for enhancing the release of the polymer into an aqueousliquid, and a viscosifying agent (e.g., an organophilic clay). Thesesuspensions, however, may be environmentally undesirable, particularlyin highly regulated regions, because the organic liquid and/or theviscosifying agents may fail to satisfy the aquatic toxicity and/orbiodegradability requirements that may be imposed in these regions.Moreover, in cement compositions that have been foamed, the organicliquid may lead to the undesired breaking of the foam, with aconcomitant release of the foaming gas, causing high formation pressuresand possible fracturing of the formation. Further, in cementcompositions, the organic liquid may not be beneficial to the propertiesof the cement, in that the organic liquids do not bind to the cement,taking up volume that could be used to enhance the cement matrix.

SUMMARY

The present invention relates to density-matched suspensions and, moreparticularly, in certain embodiments, to density-matched suspensionsthat comprise a solid particle suspended in a suspending liquid andassociated methods of use.

In one embodiment, the present invention comprises a method of treatinga subterranean formation comprising: combining components comprisingwater and a density-matched suspension to prepare a treatment fluid,wherein the density-matched suspension comprises a suspending liquid anda solid particle suspended in the suspending liquid; and introducing thetreatment fluid into a well bore that penetrates the subterraneanformation.

In another embodiment, the present invention comprises a method ofcementing in a subterranean formation comprising: combining components acement, water, and a density-matched suspension to form a cementcomposition, wherein the density-matched suspension comprises asuspending liquid and a solid particle suspended in the suspendingliquid; and introducing the cement composition into a well bore thatpenetrates the subterranean formation.

In another embodiment, the present invention comprises a methodcomprising: selecting a target density for a suspension based at leaston a solid particle to be suspended in a density-matched suspension;selecting two or more hydrophobic liquids having densities both higherand lower than the target density, wherein the hydrophobic liquidshydrolyze when placed in contact with an aqueous fluid to formhydrophilic products; combining first components comprising thehydrophobic liquids to form a mixture having about the target density;and combining second components comprising the mixture and the solidparticle to be suspended to form the density-matched suspension.

In another embodiment, the present invention comprises a suspensioncomprising: a suspending liquid comprising a hydrophobic liquid, whereinthe hydrophobic liquid hydrolyzes when placed in contact with an aqueousfluid to form one or more hydrophilic products; and a solid particlesuspended in the suspending liquid, wherein the suspension is adensity-matched suspension.

The features and advantages of the present invention will be readilyapparent to those skilled in the art. While numerous changes may be madeby those skilled in the art, such changes are within the spirit of theinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to density-matched suspensions and, moreparticularly, in certain embodiments, to density-matched suspensionsthat comprise a solid particle suspended in a suspending liquid andassociated methods of use.

There may be several potential advantages to the methods andcompositions of the present invention. One of the many potentialadvantages is that the density-matched suspensions may be more resistantto sedimentation of the solid particle than viscosity-controlledsuspensions. Another potential advantage is that the density-matchedsuspensions may be more environmentally acceptable than currentsuspensions that utilize mineral oil. For example, the suspending liquidof the density-matched suspension may comprise a hydrophobic liquid thathydrolyzes to form one or more hydrophilic compounds (e.g., alcohols,diols, etc.) that may be miscible in aqueous liquids, reducing or eveneliminating the undesired oil residue from the suspension. Without theundesired oil residue, the density-matched suspension may not lead tothe undesired breaking of a foam and, thus, may be suitable for foamingapplications, such as foamed cement compositions.

I. Examples of Density-Matched Suspensions

As previously mentioned, the density-matched suspensions generallycomprise a suspending liquid and a solid particle suspended in thesuspending liquid. As used herein, the term “density-matched suspension”refers to a suspension wherein the specific gravity of the suspendingliquid is within about 5% of the specific gravity of the solid particle.In certain embodiments, the specific gravity of the suspending liquidmay be within about 1% of the specific gravity of the solid particleand, alternatively, within about 0.1%. In contrast toviscosity-controlled suspensions-wherein settling of the suspendedparticle is prevented from settling due to viscosity-density-matchedsuspensions rely on matching of the specific gravity of the suspendingliquid and the solid particle to prevent settling. Accordingly, bymatching the specific gravity of the suspending liquid and the solidparticle, the solid particle should not have a propensity to settle.

In accordance with embodiments of the present invention, thedensity-matched suspensions may be more resistant to sedimentation ofthe solid particle than viscosity-controlled suspensions. Accordingly,the density-matched suspensions may have an extended shelf life. As usedherein, the term “shelf life” refers to the period of time a suspensioncan sit static with the suspended particles at least substantiallyhomogeneously mixed in the suspending liquid. For the purposes of thisinvention, a suspension is considered to be substantially homogenouslymixed if the concentration gradient does not adversely effect thedesired performance of the product. By way of example, a suspension maybe substantially homogenously mixed where the concentration by weight ofthe suspended particle in the top ¼ of the suspension is within about15% of the concentration by weight of the suspended particle in thebottom ¼ of the suspension, alternatively, within about 1%, andalternatively, within about 5%.

The suspensions formed in accordance with embodiments of the presentinvention allow for the matching of densities between the suspendingliquid and the solid particle suspended therein. Within certain densityrange differences between the suspending liquids and the suspendedparticle, such matching may increase the long-term stability of thesuspensions. Further, in certain embodiments, the suspending liquid maycomprise a hydrophobic liquid that may be hydrolyzed to form hydrophilicproducts when placed in contact with aqueous compositions, especiallycompositions having high or low pH, such as less than about 5 or greaterthan about 9. This may allow the incorporation of additives innon-aqueous suspensions into systems for which residual oils may beproblematic, for example, in foamed cement compositions, among others.Specifically, in foamed cement compositions used for well cementingmethods, residual oils may lead to breaking of the foam, with aconcomitant release of the foaming gas, causing high formation pressuresand possible fracturing of the formation.

In general, the suspending liquid may be any suitable liquid forsuspending the solid particle. In certain embodiments, the suspendingliquid may comprise a hydrophobic liquid. For example, the suspendingliquid may comprise a mixture of two or more hydrophobic liquids thathave different densities. In certain embodiments, hydrophobic liquidsselected may be hydrolyzed in water solutions at various pH levels toform hydrophilic compounds, e.g., alcohols and diols. The hydrolysisgenerally should eliminate the hydrophobic nature of the mixture,forming products that may be miscible in aqueous fluids. Solid particlescarried in the suspending liquid would then be deposited into theresulting aqueous fluid, for example. In certain embodiments, asurfactant included in the suspension, for example, to water wet thesolid particle and, thus, facilitate mixing of the solid particle intoan aqueous fluid. Hydrophobic liquids that may be used in embodiments ofthe present invention include, but are not limited to, cycliccarbonates, ketals, acetals, orthoesters, orthoformates, andcombinations thereof. The general chemical structures of these compoundsare shown in Formulas I-III, below, wherein Formula I represents thegeneral structural formula for a cyclic carbonate, Formula II representsthe general structural formula for a ketal or acetal, and Formula IIIrepresents the general structural formula for an orthoester ororthoformate.

A cyclic carbonate is represented by the structure shown in Formula I,in which R¹ and R² may be independently selected to be hydrogen, or analkyl group having from 1 to 5 carbons. If an alkyl group is present,the alkyl group may have additional substitutents, for example, hydroxylgroups.

In each of the structures shown in Formula II and III, R¹ may be ahydrogen or an alkyl group containing 1-5 carbons, and R²-R⁴ may beindependently selected to be alkyl groups containing 1-5 carbons. If R¹in the ketal shown in Formula II is a hydrogen group, then the compoundis called an acetal, and if R¹ in the orthoester shown in Formula III isa hydrogen group, then the compound is called an orthoformate.

Specific examples of compounds that are included in the generalstructural formulas above may include, but are not limited to, thecyclic carbonates propylene carbonate (4-methyl-1,3-dioxolan-2-one) and1,2-butylene carbonate (4-ethyl-1,3-dioxolan-2-one). The structuralformulas for these compounds is shown in Formula IV and V, below. As thedensity of propylene carbonate is around 1.200 g/cm³ (at 25° C.), andthe density of 1,2-butylene carbonate is around 1.141 g/cm³ (at 25° C.),a mixture of these two components may be used to achieve a density atany point between these two values. This density may be selected tomatch the density of a solid particle such as a hydrophilic polymer,enabling the formation of stable, long-term suspensions of the solidparticle in the suspending liquid.

As a non-limiting example of how such compounds may be used to form astable suspension, a polymer, polyacrylonitrile, may have a neat densityof about 1.183 g/cm³ (at 25° C.). In an embodiment of the presentinvention, a suspending liquid containing about 0.875 mol % propylenecarbonate and about 0.125 mol % 1,2-butylene carbonate may match thisdensity. If particles of polyacrylonitrile were suspended in thissuspending liquid, it is believed that the particles could take monthsor even years to separate from the solvent. Other effects besidesbuoyant forces may impact this stability. However, these suspendingliquids may provide higher stability than currently used suspensions inwhich the density of the solvent does not match the density of thesuspended particles and viscosity may be used to slow separation.

Other compounds from the classes discussed above may be used to obtainsuspending liquids having lower densities. Such compounds may include,for example, the orthoester 1,1,1-trimethoxyethane, having the chemicalstructure shown in Formula VI, and a density of about 0.9440 g/cm³ (at25° C.), and the ketal 2,2-dimethoxypropane, which has a density ofabout 0.8470 g/cm³ (at 25° C.), and the chemical structure shown inFormula VII.

Yet other compounds may be used in the oil mixtures to achieve higherdensities. For example, ethylene carbonate, with the chemical structureshown in Formula VIII, has a density of about 1.338 g/cm³ (at 25° C.),while glycerine carbonate, with the chemical structure shown in FormulaIX, has a density of about 1.4 g/cm³ (at 25° C.).

As noted above, the suspending liquids may be hydrolyzed to formhydrophilic products when placed in contact with aqueous fluids. Forexample, the cyclic carbonates, such as those shown in Formula I, IV, V,VIII, and IX, may quickly hydrolyze when placed in contact with aqueouscompositions having either a low pH (e.g., less than about 5) or a highpH (e.g., greater than about 9). One skilled in the art will recognizethat the hydrolysis rate of cyclic carbonates is dependent on the pH,occurring more quickly as the pH gets further away from neutral. By wayof further example, acetals or ketals, as shown in Formulas II, III, VI,and VII may quickly hydrolyze when placed in contact with water,regardless of the pH.

Solid particles that may be suspended in the suspending liquidsgenerally may have a density about the same of the density of thesuspending liquid. By way of example, where a mixture of hydrophobicliquids may be used, the solid particle may generally have densitiesbetween the upper and lower densities of the hydrophobic liquids used inthe suspending liquid, e.g., between about 0.85 g/cm³ (at 25° C.) and1.4 g/cm³ (at 25° C.) in certain embodiments. It is believed thatmatching of the density of the suspending liquid to the density of thesolid particles to be suspended would control the stability, and, thus,the effective life, of the suspension. If the densities are preciselymatched, the suspension may be stable for an indefinite period of time.If the densities are within about 1% of each other, the suspensionsshould, for example, be stable for months, or even years, before thesuspended material floats or settles out of oil mixture. If thesuspensions are within about 5% of each other, the suspensions should,for example, be stable for months. Depending on the application, thismay be sufficient.

The amount of the material that may be included in the suspensions ofthe present invention depends on, for example, the properties of thesolid particle and the desired properties of the suspension. Forexample, the solid particle may be present in the suspension in anamount in the range of about 3% to about 80% by weight of thesuspension. In some embodiments, the solid particle may be present inthe suspension in an amount in the range of about of about 10% to about50% by weight of the suspension, or alternatively of about 20% to about45% by weight of the suspension.

The suspensions of the present invention may be used in any number ofapplications where solid particles are to be suspended in a suspendingliquid for extended periods of time. For example, such applications mayinclude cosmetics (using the carbonates, for example, which have lowtoxicity), agricultural products (e.g., fertilizers, pesticides),decorative mixtures, downhole additives for oil wells, and the like. Anexemplary embodiment may use the oil mixtures of the present techniquesto make stable suspensions of fluid-loss-control additives for cementcompositions. One of ordinary skill in the art will recognize that thedensity-matched suspensions of the present techniques may be used forforming other types of additives in any number of other cementcompositions.

As described above, a suspending agent may also be included in thesuspensions of the present invention to increase the viscosity of thesuspension. While optional, the suspending agent may be used to slow theseparation of a suspended material, allowing a wider range between thedensity of the material to be suspended and the solution. Such agentsmay include hydrophobic polymers, including, but not limited to,styrene-butadiene copolymers, styrene-butadiene rubbers, polystyrene,polybutadiene, and combinations thereof. Other agents that may be usedto increase the viscosity of the suspension include organophilic clays,among others. The use of such agents may also modify the density of theoil mixture, allowing further control over the final density of thesuspension.

II. Examples of Uses of Density-Matched Suspensions in CementCompositions

In accordance with the embodiments of the present invention, cementcompositions generally may include a cement, water, and a polymericfluid-loss-control additive. As will be appreciated by those of ordinaryskill in the art, with the benefit of this disclosure, the polymericfluid-loss-control additive may have been suspended in a density-matchedsuspension prior to combination with the cement composition. In additionto polymeric fluid-loss-control additives, other solid particle includedin the cement composition may also be provided in density-matchedsuspensions, as desired.

Those of ordinary skill in the art will appreciate that the cementcompositions generally should have a density suitable for a particularapplication. By way of example, the cement composition may have adensity in the range of about 4 pounds per gallon (“lb/gal”) to about 20lb/gal. In certain embodiments, the cement compositions may have adensity in the range of about 8 lb/gal to about 17 lb/gal. Embodimentsof the cement compositions may be foamed or unfoamed or may compriseother means to reduce their densities, such as hollow microspheres,low-density elastic beads, or other density-reducing additives known inthe art. For example, a foamed cement composition may be used thatfurther comprises a gas and a surfactant for foaming and/or stabilizingthe foamed cement composition. Those of ordinary skill in the art, withthe benefit of this disclosure, will recognize the appropriate densityfor a particular application

Embodiments of the cement compositions generally comprise a cement. Avariety of cements may be utilized in these compositions, including, butnot limited to, hydraulic cements that set and harden by reaction withwater. Such cements may contain a variety of elements including calcium,aluminum, silicon, oxygen, and/or sulfur. For example, suitable cementsmay include Portland cements, pozzolana cements, gypsum cements,high-alumina-content cements, slag cements, and silica cements, amongothers, and combinations thereof. In certain exemplary embodiments, thecement may include a Portland cement. In some embodiments, the Portlandcements that are suited for use in the present techniques are classifiedas Class A, C, H, and G cements according to American PetroleumInstitute, API Specification for Materials and Testing for Well Cements,API Specification 10, Fifth Ed., Jul. 1, 1990.

The water used in embodiments of the cement compositions may befreshwater, saltwater (e.g., water containing one or more saltsdissolved therein), brine (e.g., saturated saltwater produced fromsubterranean formations), seawater, or combinations thereof. Generally,the water may be from any source, provided that it does not contain anexcess of compounds that may undesirably affect other components in thecement composition. The water may be present in an amount sufficient toform a pumpable slurry. More particularly, the water may be present inan amount in the range of about 33% and about 200% by weight of thecement (“bwoc”). In some exemplary embodiments, the water may be presentin an amount in the range of about 35% and about 70% bwoc.

As described above, the cement compositions may be foamed with a gas, incertain embodiments. The gas utilized in the foamed cement compositionsmay be any gas suitable for foaming a cement composition, including, butnot limited to, air, nitrogen, and combinations thereof. Generally, thegas should be present in the foamed cement compositions of the presenttechniques in an amount sufficient to form a suitable foam. In someembodiments, the gas may be present in an amount in the range of about10% and about 80% by volume of the composition.

Any suitable surfactant may be used in the foamed cement composition forfacilitating the foaming of a cement composition and/or also stabilizethe resultant foamed cement composition formed therewith. Suitablesurfactants may include, but are not limited to: a mixture of anammonium salt of an alkyl ether sulfate, a cocoamidopropyl betainesurfactant, a cocoamidopropyl dimethylamine oxide surfactant, sodiumchloride, and water; a mixture of an ammonium salt of an alkyl ethersulfate surfactant, a cocoamidopropyl hydroxysultaine surfactant, acocoamidopropyl dimethylamine oxide surfactant, sodium chloride, andwater; hydrolyzed keratin; a mixture of an ethoxylated alcohol ethersulfate surfactant, an alkyl or alkene amidopropyl betaine surfactant,and an alkyl or alkene dimethylamine oxide surfactant; an aqueous fluidof an alpha-olefinic sulfonate surfactant and a betaine surfactant; andcombinations thereof. An example of a suitable hydrolyzed keratin isdescribed in U.S. Pat. No. 6,547,871, the disclosure of which isincorporated herein by reference. An example of a suitable mixture of anethoxylated alcohol ether sulfate surfactant, an alkyl or alkeneamidopropyl betaine surfactant, and an alkyl or alkene dimethylamineoxide surfactant is described in U.S. Pat. No. 6,063,738, the disclosureof which is incorporated herein by reference. An example of a suitableaqueous fluid of an alpha-olefinic sulfonate surfactant and a betainesurfactant is described in U.S. Pat. No. 5,897,699, the disclosure ofwhich is incorporated herein by reference. In an embodiment, thesurfactant may include a mixture of an ammonium salt of an alkyl ethersulfate, a cocoamidopropyl betaine surfactant, a cocoamidopropyldimethylamine oxide surfactant, sodium chloride, and water.

Generally, the surfactants for foaming and/or stabilizing should bepresent in the foamed cement compositions of the present techniques inan amount sufficient to provide a suitable foam. In exemplaryembodiments, the surfactant may be present in an amount in the range ofabout 0.8% and about 10% by volume of the water (“bvow”) present in thefoamed cement composition.

As previously discussed, fluid-loss-control additives often may beprovided in oil-based suspensions containing suspended hydrophilicpolymers, in addition to other ingredients, such as clays, surfactants,and other components. These suspensions generally allow more efficientdistribution of the additives, for example, the liquid suspensions maybe injected under pressure into a pipeline containing a flowing streamof cement slurry. However, the long-term storage of these suspensionsmay be problematic. For instance, polymer suspensions tend to separateover time, with the polymer particles settling or floating out of thesolution. The separated particles contact each other and may form agelled mass, for example. This gel may be very difficult to remix into ahomogeneous solution, for example, leading to a varying amount ofsuspended polymer being injected into the flowstream, or in addition thesettled material may lead to less active product available for use inthe suspension and the concurrent loss of product at the bottom or topof tanks and vessels. If the product is not used within a few months, incertain embodiments, such separation may prevent the product from beingused at all, requiring expensive disposal. Further, the oil componentsin these suspensions may tend to destabilize foams, releasing the gasfrom foamed cement compositions. The destabilization of the foamedcement composition may exert excessive hydrostatic pressure on thesubterranean formation so as to unintentionally fracture the formation.Additional ingredients, such as the organophilic clay, are typicallyused to increase the viscosity of these oil-based solutions, which mayslow the separation of the polymers, extending the shelf life. Further,other ingredients, such as surfactants, may aid in affecting the releaseof the hydrophilic polymers from the oil-based solution into the aqueouscement composition.

In contrast to previous formulations, the density-matched suspensionsmade in accordance with embodiments of the present invention may be morestable, for example, due to the matching of densities of the suspendingliquid and the solid particle. Thus, while suspending agents may be usedto increase the viscosity of the suspending liquids, these ingredientsare optional. Further, in certain embodiments, hydrolysis of thesuspending liquid when placed in contact with a high-pH material, suchas a cement mixture, deposits the solid particle directly into thecement composition where they may fully hydrate, for example.Accordingly, while surfactants may be used to decrease the time requiredto transfer the hydrophilic polymer into the aqueous cement composition,these components may also be optional. In certain embodiments,hydrolysis of the suspending liquid results in the formation ofwater-soluble products, such as diols, there may be no residual oil todestabilize the foamed cement composition.

Polymeric fluid-loss-control additives that may be used in thedensity-matched suspensions in accordance with embodiments of thepresent invention may generally have densities about the same as thesuspending liquid. Where a mixture of hydrophobic liquids are used, forexample, the polymeric fluid-loss-control additive may have a densitybetween the upper and lower densities of the hydrophobic liquids used inthe suspending liquid, e.g., between about 0.85 g/cm³ (at 25° C.) and1.4 g/cm³ (at 25° C.) in certain embodiments. For example, types ofpolymers that may be used in the present techniques include, but are notlimited to: cellulose derivatives such as those having densities betweenabout 1.27 g/cm³ (at 25° C.) and 1.37 g/cm³ (at 25° C.), or about 1.32g/cm³ (at 25° C.); modified-acrylamide copolymers such as those havingdensities between about 1.30 g/cm³ (at 25° C.) and 1.40 g/cm³ (at 25°C.), or about 1.37 g/cm³ (at 25° C.); acrylic copolymers such as thosehaving densities between about 1.30 g/cm³ (at 25° C.) and 1.40 g/cm³ (at25° C.), or about 1.37 g/cm³ (at 25° C.); and polyvinylpyrrolidonecopolymers such as those having densities between about 1.25 g/cm³ (at25° C.) and 1.35 g/cm³ (at 25° C.), or about 1.30 g/cm³ (at 25° C.).Other types of materials having higher or lower densities may also beused in embodiments of the density-matched suspensions with the additionof materials to modify the density and/or viscosity of the solution, asdiscussed below.

Examples of suitable polymeric fluid-loss-control additives that may beused in embodiments of the density-matched suspensions include, but arenot limited to: guar gum; hydroxyethyl guar; hydroxypropyl guar;carboxymethyl guar; carboxymethylhydroxyethyl guar;carboxymethylhydroxypropyl guar; cellulose derivatives; lignin orlignite grafted with polymers comprising at least one monomer selectedfrom the group consisting of 2-acrylamido-2-methylpropanesulfonic acid,acrylonitrile and N,N-dimethylacrylamide; hydroxyethyl cellulose;carboxyethylcellulose; carboxymethylcellulose;carboxymethylhydroxyethylcellulose; cellulose grafted with an allylic ora vinylic monomers; polyacrylate; polymethacrylate; polyacrylamide;polyvinyl alcohol; and polyvinylpyrrolidone. Further, the polymers mayalso include copolymers, derivatives, and graft copolymers of thepolymers listed above. Other suitable polymers that may be used inembodiments of the density-matched suspensions include, but are notlimited to: (1) a copolymer comprising acrylamide,N-vinyl-N-methylacetamide, and sodium salt of vinyl sulfonate; (2) acopolymer comprising partially hydrolyzed acrylamide,N-vinyl-N-methylacetamide, and 2-acrylamido-2-methylpropane sulfonicacid salt; (3) a copolymer comprising 2-acrylamido-2-methylpropanesulfonic acid salt, N-vinyl-N-methylacetamide, and acrylamide; and (4) acopolymer comprising 2-acrylamido-2-methylpropane sulfonic acid salt,acrylamide, N-vinylpyrrolidone, and acrylic acid.

Suitable polymeric fluid-loss control additives useful in embodiments ofthe cement compositions of the present techniques may include any of theabove-described polymers, copolymers, or combinations thereof. Thepolymeric fluid-loss-control additive should generally be included inthe cement compositions of the present techniques in an amountsufficient to provide the desired fluid-loss control. For example, thepolymeric fluid-loss-control additive may be present in an amount in therange of about 0.25% and about 5% bwoc.

Other additives suitable for use in subterranean cementing operationsalso may be added to embodiments of the cement compositions. Examples ofsuch additives include, but are not limited to, strength-retrogressionadditives, set accelerators, weighting agents, weight-reducingadditives, heavyweight additives, lost-circulation materials,filtration-control additives, dispersants, defoaming agents, andcombinations thereof. Specific examples of these, and other, additivesinclude crystalline silica, amorphous silica, salts, fibers, hydratableclays, vitrified shale, microspheres, fly ash, lime, latex, thixotropicadditives, combinations thereof and the like. A person having ordinaryskill in the art, with the benefit of this disclosure, will readily beable to determine the type and amount of additive useful for aparticular application and desired result.

The cement compositions of the present techniques may be prepared inaccordance with any suitable technique. For example, the cementcomposition may be prepared by combining at least cement, water, and adensity-matched suspension, wherein the suspension comprises asuspending liquid and solid particle suspended in the suspending liquid.In certain embodiments, the solid particle comprises a polymericfluid-loss-control additive. In certain embodiments, the suspendingliquid may comprise a mixture of two or more hydrophobic liquids thatmay, for example, hydrolyze when placed in contact with an aqueousliquid to form one or more hydrophilic products. The cement and water,for example, may be combined and mixed for a sufficient period of timeto form a pumpable cement composition. Liquid additives, if any, may bemixed with the water prior to combination with the cement, in certainembodiments. For example, the density-matched suspension may be mixedwith the water prior to combination with the cement. Alternatively,liquid additives (such as the density-matched suspension) may be addedwhile mixing the cement and water. Dry solid additives, if any, may bedry blended with the cement prior to combination with the water. Incertain embodiments, the cement composition then may be pumped to thewell bore. If foamed, the surfactant followed by the gas may be injectedinto the cement composition as the cement composition is being pumped.One of ordinary skill in the art, with the benefit of this disclosure,will recognize other suitable techniques for preparing the cementcompositions of the present techniques.

An example of a method of cementing of the present invention comprises:combining at least a cement, water, and a density-matched suspension toform a cement composition, wherein the density-matched suspensioncomprises a suspending liquid and a solid particle suspended in thesuspension liquid; and introducing the cement composition into a wellbore. In certain embodiments, the cement composition may a foamed cementcomposition and further comprise a gas and a surfactant for foamingand/or stabilizing the foamed cement composition, as set forth above.The location to be cemented may be any suitable location, including aspace between a wall of the well bore and a conduit disposed therein.

Furthermore, while the proceeding discussion is generally directed tothe use of density-matched suspensions in cementing methods, those ofordinary skill in the art, with the benefit of this disclosure, willappreciate that the present technique also encompasses the use of suchdensity-matched suspensions in any variety of different subterraneantreatments. For example, the suspensions may be included in any numberof well treatment fluids, including, but not limited to, drillingfluids, completion fluid, stimulation fluids and clean-up fluids. Suchtreatment fluids optionally may comprise any number of additionaladditives, including, but not limited to, salts, surfactants,fluid-loss-control additives, gas, nitrogen, carbon dioxide,surface-modifying agents, tackifying agents, foamers, corrosioninhibitors, scale inhibitors, catalysts, clay control agents, biocides,friction reducers, antifoam agents, bridging agents, dispersants,flocculants, H₂S scavengers, CO₂ scavengers, oxygen scavengers,lubricants, viscosifying agents, breakers, weighting agents (e.g.,barite), relative permeability modifiers, resins, particulate materials(e.g., proppant particulates), wetting agents, coating enhancementagents, and the like. Examples of suitable viscosifying agents, include,but are not limited to, colloidal agents (e.g., clays such as bentonite,polymers, guar gum), emulsion-forming agents, diatomaceous earth,biopolymers, synthetic polymers, chitosans, starches, gelatins, andmixtures thereof.

In addition, while the preceding discussion is directed todensity-matched suspensions that comprise a polymeric fluid-loss-controladditive suspended in a suspending liquid, those of ordinary skill inthe art, with the benefit of this disclosure, will appreciate that thedensity-matched suspensions may be used to deliver a variety of otherdownhole additives used in particulate form, in accordance withembodiments of the present technique. By way of example, viscosifiers,cement set retarders, lost-circulation materials, swellable elastomers,and other solid-particulate additives may be suspended in adensity-matched suspension, in accordance with embodiments of thepresent invention.

To facilitate a better understanding of the present invention, thefollowing examples of certain aspects of some embodiments are given. Inno way should the following examples be read to limit, or define, theentire scope of the invention.

EXAMPLES

To demonstrate settling of solid particles in different fluids, twosamples were prepared. In a 250-mL jar, 10 g of a modified-acrylamidecopolymer (HALAD® 344 fluid-loss additive, available from HalliburtonEnergy Services, Inc.) (SG 1.2) was placed in 160 mL of propylenecarbonate and 40 mL of butylene carbonate (SG 1.19). As a control, inanother 250-mL jar, 10 g of the modified-acrylamide copolymer (same) wasplaced in 200 mL of mineral oil (SG 0.88). Both jars were placed on astir plate and fully mixed with a stir bar and spatula. The viscosity ofeach suspension was measured using a FANN® viscometer. The viscositymeasurements are provided in the table below.

TABLE 1 FANN ® Viscometer Readings RPM Carbonate Suspension Mineral OilSuspension 600 8 215 300 4.5 113 200 3 78 100 1.5 41

After the viscosity measurements, each sample was left static at roomtemperature for 24 hours. Although both samples showed settling, thecarbonate suspension showed less propensity to settle. Although themineral oil suspension was thicker, virtually all of the polymer hadsettled in the mineral oil. In the carbonate suspension, there was somesettling, but much of the polymer was still in suspension. Also, byplacing the carbonate suspension back on the stir plate, the settledpolymer was easily re-suspended. However, the mineral oil suspension didnot easily re-suspend by placement on the stir plate without additionalagitation from a spatula.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered ormodified and all such variations are considered within the scope andspirit of the present invention. All numbers and ranges disclosed abovemay vary by any amount (e.g., 1 percent, 2 percent, 5 percent, or,sometimes, 10 to 20 percent). Whenever a numerical range with a lowerlimit and an upper limit is disclosed, any number and any included rangefalling within the range is specifically disclosed. In particular, everyrange of values (of the form, “from about a to about b,” or,equivalently, “from approximately a to b,” or, equivalently, “fromapproximately a-b”) disclosed herein is to be understood to set forthevery number and range encompassed within the broader range of values.Moreover, the indefinite articles “a” or “an”, as used in the claims,are defined herein to mean one or more than one of the element that itintroduces. Also, the terms in the claims have their plain, ordinarymeaning unless otherwise explicitly and clearly defined by the patentee.

1. A method of treating a subterranean formation comprising: combiningcomponents comprising water and a density-matched suspension to preparea treatment fluid, wherein the density-matched suspension comprises asuspending liquid and a solid particle suspended in the suspendingliquid; and introducing the treatment fluid into a well bore thatpenetrates the subterranean formation.
 2. The method of claim 1, whereinthe treatment fluid comprises at least one fluid selected from the groupconsisting of a drilling fluid, a stimulation fluid, a clean-up fluid,and a cement composition.
 3. The method of claim 1 wherein thesuspending liquid comprises a hydrophobic liquid.
 4. The method of claim1, wherein the suspending liquid comprises a hydrophobic liquid thathydrolyzes when placed in contact with an aqueous liquid to form one ormore hydrophilic products. 5 The method of claim 1, wherein thesuspending liquid comprises at least one hydrophobic liquid selectselected from the group consisting of an acetal, a ketal, and anorthoester.
 6. The method of claim 1, wherein the suspending liquidcomprises at least one hydrophobic liquid select selected from the groupconsisting of propylene carbonate, butylene carbonate, ethylenecarbonate, and a glycerin carbonate.
 7. The method of claim 1, whereinthe suspending liquid comprises a mixture of hydrophobic liquids,wherein the mixture hydrolyzes when placed in contact with an aqueousliquid to form one or more hydrophilic products.
 8. The method of claim7, wherein the mixture hydrolyzes when the pH of the aqueous fluid isgreater than about
 9. 9. The method of claim 7, wherein the mixturehydrolyzes when the pH of the aqueous fluid is less than about
 5. 10.The method of claim 8, wherein the density of the mixture is withinabout 1% of the density of the solid particle suspending in the mixture.11. The method of claim 1, wherein suspending liquid comprises a mixtureof cyclic carbonates.
 12. The method of claim 1, wherein thedensity-matched suspension comprises a suspending agent.
 13. The methodof claim 1, wherein the density-matched suspension comprises anorganophilic clay.
 14. The method of claim 1, wherein the solid particlecomprises a polymeric fluid-loss-control additive.
 15. The method ofclaim 1, wherein the solid particle has a density in the range of 0.85grams per cubic centimeter to 1.4 grams per cubic centimeter.
 16. Themethod of claim 1, wherein the solid particle is present in thedensity-matched suspension in an amount in the range of 10% to about 70%by weight of the suspension.
 17. The method of claim 1 comprisingselecting a target density for the density-matched suspension based atleast on the solid particle; selecting two or more hydrophobic liquidshaving densities both higher and lower than the target density;combining components comprising the hydrophobic liquids in anappropriate ratio to form the suspending liquid having about the targetdensity; and combining at least the suspending liquid and the solidparticle to form the density-matched suspension.
 18. The method of claim1, wherein the treatment fluid comprises a cement, wherein thesuspending liquid comprise a mixture of two or more cyclic carbonates,and wherein the solid particle comprises a polymer.
 19. A method ofcementing in a subterranean formation comprising: combining componentscomprising cement, water, and a density-matched suspension to form acement composition, wherein the density-matched suspension comprises asuspending liquid and a solid particle suspended in the suspendingliquid; and introducing the cement composition into a well bore thatpenetrates the subterranean formation.
 20. The method of claim 19wherein the density-matched suspension is combined with the water priorto or at the same time as the cement is combined with the water.
 21. Themethod of claim 19, wherein the suspending liquid comprises a mixture ofhydrophobic liquids, wherein the mixture hydrolyzes when placed incontact with an aqueous liquid at a pH of greater than about 9 to formone or more hydrophilic products.
 22. The method of claim 21, whereinthe cement composition is foamed.
 23. The method of claim 21, whereinthe density of the mixture is within about 5% of the density of thesolid particle suspended in the mixture.
 24. The method of claim 19,wherein suspending liquid comprises a mixture of cyclic carbonates. 25.A method comprising: selecting a target density for a suspension basedat least on a solid particle to be suspended in a density-matchedsuspension; selecting two or more hydrophobic liquids having densitiesboth higher and lower than the target density, wherein the hydrophobicliquids hydrolyze when placed in contact with an aqueous fluid to formhydrophilic products; combining first components the hydrophobic liquidsto form a mixture having about the target density; and combining secondcomponents comprising the mixture and the solid particle to be suspendedto form the density-matched suspension.
 26. A suspension comprising: asuspending liquid comprising a hydrophobic liquid, wherein thehydrophobic liquid hydrolyzes when placed in contact with an aqueousfluid to form one or more hydrophilic product; and a solid particlesuspended in the suspending liquid, wherein the suspension is adensity-matched suspension.